1. Field of the Invention
The present invention relates generally to small particle copper pyrithione compositions, and a method of preparing these compositions. Preferably the compositions are provided in a non-dusting form as a dispersion of the small particles in an aqueous or organic solvent carrier. Alternatively, the small particles are provided in the form of a solid powder for use in facilities equipped to avoid or minimize human exposure to, and handling of, the powder. The small particle copper pyrithione compositions are suitable for use as antifouling agents in antifouling paints, such as marine paints. These small particles exhibit enhanced storage stability in dispersions with liquid media, as well as an enhanced leach rate from the antifouling paints, relative to larger size copper pyrithione particles.
2. Description of the Related Art
Pyrithione salts are well known compounds that are useful in a wide variety of applications including their use biocides, such as fungicides and bactericides. Heavy metal salts of pyrithione, including zinc, tin, cadmium and zirconium, as well as the magnesium and aluminum salts, have been produced in the form of flat platelets suitable for use in shampoo, are disclosed in U.S. Pat. Nos. 4,345,080 and 4,323,683.
Small particles of metal salts of pyrithione have been disclosed for use on the skin and hair. Illustratively, U.S. Pat. No. 4,670,430 discloses polyvalent metal salts of 2-mercaptopyridine-N-oxide in the form of a fine powder of particles in which at least fifty percent of the particles have a particle size below 0.2 micron. The '430 patent discloses that, when this fine particle of particles is incorporated into shampoo or rinse compositions, the dispersion stability of these salts is improved and the adsorbability of the particles onto the skin and hair is enhanced. Another illustration of the use of small particles of metal pyrithiones in hair treatment is provided in U.S. Pat. No. 5,723,112. The '112 patent discloses an antimicrobial hair treatment composition comprising (a) a surfactant, (b) fine particles of an insoluble particulate metal pyrithione in which at least 90% by weight of the particles have a size of five microns or less, and (c) a polymeric cationic deposition aid for the small particles.
Pyrithiones have also been used as antimicrobial additives in a variety of paints. Illustratively, various paints containing a pyrithione salt (e.g. zinc or sodium pyrithione) plus a copper salt (e.g. cuprous oxide or cuprous thiocyanate) are known in the art, as disclosed, for example, in U.S. Pat. No. 5,057,153. As another illustration, U.S. Pat. No. 5,185,033 describes a process for making a paint or paint base containing copper pyrithione or pyrithione disulfide plus cuprous oxide, wherein the paint exhibits stability against gelation during storage. As yet another illustration, U.S. Pat. No. 5,246,489 discloses a process for providing in situ generation of copper pyrithione in a paint or paint base which comprises incorporating a metal salt of pyrithione, cuprous oxide and a controlled amount of water into the paint either during or after the formation of the paint.
In many applications, copper pyrithione offers several advantages over other forms of pyrithione such as zinc pyrithione. For example, copper pyrithione is more stable than zinc pyrithione when added to paint products, and therefore is less likely to cause gelation during storage.
Commercially available copper pyrithione is typically sold as a dry powder. Generally, the particle size range for this commercial dry powder is between about 0.8 micron and about 30 microns, with a median particle size of from 3 to 6 microns. A key disadvantage of this commercial powder is that it generates dust during handling, necessitating special handling equipment, particularly since copper pyrithione powder was shown to be more toxic than zinc pyrithione powder when tested for acute inhalation toxicity in rats. This dusting issue associated with copper pyrithione dry powder is addressed in PCT publication WO00/54589. This publication discloses resolving the dusting issue using dispersions of solid copper pyrithione in a liquid dispersing medium.
The present inventors have now observed that, in use, although the dispersions of the PCT publication WO00/54589 obviate the dusting issue, they are subject to another problem. More specifically, paints made with these dispersions tend to provide a decreased leaching rate of copper pyrithione out of the paint in a low temperature environment. Such decreased leaching increases the likelihood that not enough antifouling agent will leach from the paint to prevent marine fouling at the paint's surface. The present invention provides one solution to this decreased leach rate problem, thereby insuring desired low temperature antifouling efficacy for copper pyrithione-containing antifouling paints.